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Optimization of the WLS design for positron emission mammography and Total-Body J-PET systems

Georgadze Anzori, Shivani Shivani, Ardebili Keyvan Tayefi, Moskal Paweł

Bio-Algorithms and Med-Systems

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2023

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Vol. 19, no. 1

114--123

EN

Total-body positron emission tomography (PET) instruments are medical imaging devices that detect and visualize metabolic activity in the entire body. The PET scanner has a ring-shaped detector that surrounds the patient and detects the gamma rays emitted by the tracer as it decays. Usually these detectors are made up of scintillation crystals coupled to photodetectors that convert the light produced by the scintillation crystal into electrical signals. Jagiellonian Positron Emission Mammograph (J-PEM) is the first J-PET prototype module based on a novel idea with a plastic scintillator and wavelength shifter (WLS). At the same time, it is a prototype module for the Total-Body J-PET system. J-PEM can be an effective system for the detection and diagnosis of breast cancer in its early stage by improving sensitivity. This can be achieved using the superior timing properties of plastic scintillators combined with the WLS sheets readout. In this paper we present an application of the Geant4 program for simulating optical photon transport in the J-PEM module. We aim to study light transport within scintillator bars and WLS sheets to optimize gamma-ray hit position resolution. We simulated a pencil beam of 511 keV photons impinging the scintillator bar at different locations. For each condition we calculated the value of the pulse height centroid and the spread of the photon distribution. Some free parameters of the simulation, like reflectivity and the effective attenuation length in the sheet, were determined from a comparison to experimental data. Finally, we estimated the influence of the application of WLS layer in the Total-Body J-PET on the scatter fraction. To optimize the performance of the J-PEM module we compared geometry WLS strips 50 and 83. It was found that spatial resolution was 2.7 mm and 3.5 mm FWHM for 50 and 83 WLS strips, respectively. Despite the better granularity, the 83-strip WLS geometry exhibited poorer resolution due to fewer photons being transmitted to the strip, resulting in large fluctuations of signal.

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Evaluation of Modular J-PET sensitivity

Tayefi Ardebili Faranak, Niedźwiecki Szymon, Moskal Paweł

Bio-Algorithms and Med-Systems

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2023

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Vol. 19, no. 1

132--138

EN

The Modular J-PET represents the latest advancement in the Jagiellonian-PET series, utilizing extended plastic scintillator strips. This prototype's modular design enables cost-effective imaging of multi-photon annihilation and positronium, allowing for easy assembly, portability, and versatility. Additionally, its lightweight construction facilitates static bed examinations with a mobile detection system that can be positioned conveniently alongside the patient, negating the requirement for spacious clinical settings. Comprising 24 modules arranged in regular 24-sided polygons circumscribing a 73.9 cm diameter circle, each module integrates 13 scintillator strips, measuring 50 cm in length and 6 mm × 24 mm in cross-section. Scintillation light is captured at both ends through analog Silicon Photomultipliers (SiPMs). This research presents Sensitivity of the Modular J-PET tomograph, adhering to the NEMA_NU 2-2018 standards. Sensitivity measurement was performed with 68Ge line source inside the 5 sleeves aluminium phantom placed at center of the detector`s field-of-view (FOV) and 10 cm offset from the center of detector. Analyzing the gathered data involved employing the specialized J-PET Framework software, developed within the C++ architecture. To validate the experimental findings, comparisons were made with GATE simulations, wherein the source and phantom were emulated in the same configuration as employed in the actual experiment. The system sensitivity of the Modular J-PET was assessed to be 1.03 ± 0.02 cps/kBq in the center of the detector`s FOV with the peak sensitivity of 2.1 cps/kBq. However, the simulations indicate that at the center of the detector's FOV, the Modular J-PET achieves a system sensitivity of 1.32 ± 0.03 cps/kBq, with a peak sensitivity of 2.9 cps/kBq.

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Cross-sections and gamma-yields in (p, x) reactions on 14N and 16O for 14,15O production

Kadenko Ihor, Sakhno Nadiia V., Moskal Pawel

Bio-Algorithms and Med-Systems

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2023

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Vol. 19, no. 1

139--143

EN

Dose delivery in proton beam therapy requires significant effort for in vivo verification. PET is considered as one of the most precise methods for such verification using short- -lived radionuclides. One of the newer approaches in proton therapy is based on FLASH therapy, when a 40-60 Gy absorbed dose could be delivered in millisecond time intervals. For this very promising type of therapy a very important task is to reliably identify the beam stopping position within the corresponding organ with a tumor in the patient’s body. This could be done if the beam proton energy in the body is still above the threshold of the corresponding nuclear reaction, in the outgoing channel of which will be produced positron-emitting nuclei. In this work we consider the production of oxygen radionuclides emitting positrons 14O (the half-life 70.6 s) and 15O (the half-life 122.2 s). Using the TALYS code, we calculated cross sections of proton-induced nuclear reactions on 14N and 16O, leading to the formation of 14,15O with the application of a well- -working optical model. In addition, we calculated total gamma-production and average gamma-emission energy for incident proton energy 150 MeV.

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A cross-staged gantry for total-body PET and CT imaging

Kaplanoğlu Muhammed Tevfik, Moskal Paweł

Bio-Algorithms and Med-Systems

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2023

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Vol. 19, no. 1

109--113

EN

Total-body Positron Emission Tomography (PET) scanning is a promising new method for rapidly acquiring comprehensive wide-volume metabolic data with a lower radiation dosage compared to discrete whole-body PET imaging. PET scanners are generally used with Computed Tomography (CT) scanners to precisely understand tumor location and composition with the help of anatomical images. However, PET/CT sequential imaging methods for simultaneous total-body imaging are impractical for claustrophobic patients due to the enclosed gantry design and require large examination rooms because of the need for an exceptionally long patient table. To address this challenge, the Jagiellonian-PET Tomography (J-PET) Total-body scanner employs an innovative approach: utilizing both PET and CT devices on the same patient table but from different axes. The motion system of the J-PET Total Body scanner requires custom linear stages to move both PET and CT gantries. In this study, a novel cross-staged linear guiding solution is proposed by combining scanners on intersecting separable stages. The proposed sliding system is a combination of different machine elements and will be produced for the J-PET Total-body PET/CT Scanner. Concept designs are shown, and the proposed system is described. The application of the system for the J-PET total-body PET/CT scanner is discussed. The proposed solution is still in the development phase. The system holds the potential to achieve combining CT and PET scanners from different axes and enables motion artifact-free imaging for total-body imaging.

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Towards high sensitivity and high-resolution PET scanners: imaging-guided proton therapy and total body imaging

Lang Karol

Bio-Algorithms and Med-Systems

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2022

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Vol. 18, no. 1

96--106

EN

Quantitative imaging (i.e., providing not just an image but also the related data) guidance in proton radiation therapy to achieve and monitor the precision of planned radiation energy deposition field in-vivo (a.k.a. proton range verification) is one of the most underinvested aspects of radiation cancer treatment despite that it may dramatically enhance the treatment accuracy and lower the exposure related toxicity improving the entire outcome of cancer therapy. In this article, we briefly describe the effort of the TPPT Consortium (a collaborative effort of groups from the University of Texas and Portugal) on building a time-of-flight positronemission-tomography (PET) scanner to be used in preclinical studies for proton therapy at MD Anderson Proton Center in Houston. We also discuss some related ideas towards improving and expanding the use of PET detectors, including the total body imaging.

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Positronium as a biomarker of hypoxia

Moskal Paweł, Stępień Ewa Ł.

Bio-Algorithms and Med-Systems

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2021

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Vol. 17, no. 4

311--319

EN

In this review article, we present arguments demonstrating that the advent of high sensitivity total-body PET systems and the invention of the method of positronium imaging, open realistic perspectives for the application of positronium as a biomarker for in-vivo assessment of the degree of hypoxia. Hypoxia is a state or condition, in which the availability of oxygen is not sufficient to support physiological processes in tissue and organs. Positronium is a metastable atom formed from electron and positron which is copiously produced in the intramolecular spaces in the living organisms undergoing positron emission tomography (PET). Properties of positronium, such as e.g., lifetime, depend on the size of intramolecular spaces and the concentration in them of oxygen molecules. Therefore, information on the partial pressure of oxygen (pO2) in the tissue may be derived from the positronium lifetime measurement. The partial pressure of oxygen differs between healthy and cancer tissues in the range from 10 to 50 mmHg. Such differences of pO2 result in the change of ortho-positronium lifetime e.g., in water by about 2–7 ps. Thus, the application of positronium as a biomarker of hypoxia requires the determination of the mean positronium lifetime with the resolution in the order of 2 ps. We argue that such resolution is in principle achievable for organ-wise positronium imaging with the total-body PET systems.